The purpose of this project, entitled "Conduct of Studies to Evaluate the Toxicological and Carcinogenic Potential of Selected Chemicals - Riddelline, o-Nitrotoluene, m-Nitrotoluene, p-Nitrotoluene, 2,4- Decadienal, and 2,4-Hexadienal in Laboratory Animals", is to provide for the testing of these six chemicals for the NTP Program. The objective is to continue to characterize the toxicologic effects of chemical and physical substance through studies in animals. The typical approach is repeated administration of the agent to groups of animals for variable periods up to two years or more with clinical, toxicologic and pathologic evaluation of the adverse health effects by comparison with groups of control animals. The second phase of this contract, following the developmental efforts in the base contract, will involve the actual conduct of the prechronic and chronic toxicity/carcinogenicity studies.